Underwater 'tree rings': Calcite crusts of arctic algae record 650 years of sea ice change

Nov 18, 2013

Almost 650 years of annual change in sea-ice cover can been seen in the calcite crust growth layers of seafloor algae, says a new study from the University of Toronto Mississauga (UTM).

"This is the first time coralline have been used to track changes in Arctic sea ice," says Jochen Halfar, an associate professor in UTM's Department of Chemical and Physical Sciences. "We found the algal record shows a dramatic decrease in ice cover over the last 150 years."

With colleagues from the Smithsonian Institution, Germany and Newfoundland, Halfar collected and analyzed samples of the alga Clathromorphum compactum. This long-lived plant species forms thick rock-like calcite crusts on the seafloor in shallow waters 15 to 17 metres deep. It is widely distributed in the Arctic and sub-Arctic Oceans.

Divers retrieved the specimens from near-freezing seawater during several research cruises led by Walter Adey from the Smithsonian.

The algae's growth rates depend on the temperature of the water and the light they receive. As snow-covered sea ice accumulates on the water over the algae, it turns the sea floor dark and cold, stopping the plants' growth. When the sea ice melts in the warm months, the algae resume growing their calcified crusts.

This continuous cycle of dormancy and growth results in visible layers that can be used to determine the length of time the algae were able to grow each year during the ice-free season.

This video is not supported by your browser at this time.

"It's the same principle as using rings to determine a tree's age and the levels of precipitation," says Halfar. "In addition to ring counting, we used radiocarbon dating to confirm the age of the algal layers."

After cutting and polishing the algae, Halfar used a specialized microscope to take thousands of images of each sample. The images were combined to give a complete overview of the fist-sized specimens.

Halfar corroborated the length of the algal growth periods through the magnesium levels preserved in each growth layer. The amount of magnesium is dependent on both the light reaching the algae and the temperature of the sea water. Longer periods of open and warm water result in a higher amount of algal magnesium.

During the Little Ice Age, a period of global cooling that lasted from the mid-1500s to the mid-1800s, the algae's annual growth increments were as narrow as 30 microns due to the extensive sea-ice cover, Halfar says. However, since 1850, the thickness of the algae's growth increments have more than doubled, bearing witness to an unprecedented decline in sea ice coverage that has accelerated in recent decades.

Halfar says the represent not only a new method for climate reconstruction, but are vital to extending knowledge of the climate record back in time to permit more accurate modeling of future climate change.

Currently, observational information about annual changes in the Earth's temperature and climate go back 150 years. Reliable information about comes from satellites and dates back only to the late 1970s.

"In the north, there is nothing in the shallow oceans that tells us about climate, water temperature or coverage on an annual basis," says Halfar. "These algae, which live over a thousand years, can now provide us with that information."

The research was published in the Proceedings of the National Academy of Sciences.

Explore further: Polar ecosystems vulnerable to sunlight

More information: Arctic sea-ice decline archived by multicentury annual-resolution record from crustose coralline algal proxy, www.pnas.org/cgi/doi/10.1073/pnas.1313775110

Related Stories

Antarctic sea ice thickness affects algae populations

Dec 18, 2012

In the waters off Antarctica, algae grow and live in the sea ice that surrounds the southern continent-a floating habitat sure to change as the planet warms. As with most aquatic ecosystems, microscopic algae form the base ...

Polar ecosystems vulnerable to sunlight

Jul 31, 2013

(Phys.org) —Slight changes in the timing of the annual loss of sea-ice in polar regions could have dire consequences for polar ecosystems, by allowing a lot more sunlight to reach the sea floor.

Declining sea ice to lead to cloudier Arctic: study

Mar 31, 2012

Arctic sea ice has been declining over the past several decades as global climate has warmed. In fact, sea ice has declined more quickly than many models predicted, indicating that climate models may not be correctly representing ...

Why is Antarctic sea ice growing?

Oct 29, 2013

Recently NASA reported that this year's maximum wintertime extent of Antarctic sea ice was the largest on record, even greater than the previous year's record. ...

Novel testing device for detecting toxic blue-green algae

Jun 24, 2013

VTT Technical Research Centre of Finland has developed a fast and affordable testing device for detecting the presence of toxic blue-green algae in water. There is currently no fast, affordable and user-friendly way for consumers ...

Recommended for you

Image: Grand Canyon geology lessons on view

5 hours ago

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of ...

First radar vision for Copernicus

5 hours ago

Launched on 3 April, ESA's Sentinel-1A satellite has already delivered its first radar images of Earth. They offer a tantalising glimpse of the kind of operational imagery that this new mission will provide ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

RobL
1 / 5 (2) Nov 18, 2013
It is interesting that the 'relative' dramatic decrease in sea ice cover time-span is described as the last '150' years.

I wish the article explained how the other factor like nutrient abundance / flux were ruled out.
orti
1 / 5 (2) Nov 19, 2013
Yes. The 150 years part is interesting. I thought AGW got into gear 50 years ago.

More news stories

Tiny power plants hold promise for nuclear energy

Small underground nuclear power plants that could be cheaper to build than their behemoth counterparts may herald the future for an energy industry under intense scrutiny since the Fukushima disaster, the ...

Unraveling the 'black ribbon' around lung cancer

It's not uncommon these days to find a colored ribbon representing a disease. A pink ribbon is well known to signify breast cancer. But what color ribbon does one think of with lung cancer?